The present invention relates to a polishing apparatus, more precisely relates to a polishing apparatus having an outer pin gear and an inner pin gear so as to rotate a carrier holding a workpiece.
Polishing apparatuses are used for simultaneously polishing both side faces of workpieces, e.g., wafer. In such polishing apparatus, a carrier or carriers holding workpieces are rotated between a lower polishing plate and an upper polishing plate, which are independently driven. Therefore, the both side faces of the workpieces can be simultaneously polished.
As shown in FIG. 4, an internal gear 204 and a sun gear 206, which is located at the center of the internal gear 204, are used for rotating carriers 208.
The internal gear 204 and the sun gear 206 are independently rotated. Plate-shaped carriers 208 have outer gear teeth, which are formed on an outer circumferential face thereof. The outer gear teeth are engaged with an inner gear section of the internal gear 204 and an outer gear section of the sun gear 206. With this structure, the carriers 208 are rotated on their axes and moved around the sun gear 206.
As described above, a plurality of the carriers 208 are provided between the internal gear 204 and the sun gear 206, and a plurality of through-holes 207, in which workpieces are held, are formed in each of the carriers 208. Therefore, many workpieces can be polished simultaneously.
In the above described conventional polishing apparatus, the inner gear section of the internal gear 204 and the outer gear section of the sun gear 206 are much-abraded. To solve the problem, an improved polishing apparatus was invented (see Japanese Patent Gazette No. 9-239657).
The improved polishing apparatus has an outer pin gear, which acts as the internal gear, and an inner pin gear, which acts as the sun gear. An outer gear section of the inner pin gear is constituted by a plurality of gear teeth, which are arranged along an outer circumferential face of the inner pin gear. Further, an inner gear section of the outer pin gear is constituted by a plurality of gear teeth, which are arranged along an inner circumferential face of the outer pin gear. Outer gear teeth of carriers are engaged with the inner gear section of the outer pin gear and the outer gear section of the inner pin gear, so that the carriers are rotated on their axes and moved around the inner pin gear.
FIG. 5 is a partial sectional view of the inner pin gear, which shows one gear tooth 306a. 
A through-hole 306c is formed in an inner pin ring 306b, which is a main body of the inner pin gear. A pin 314 is pierced through the through-hole 306c from the bottom side and fixed by a nut 315. The pin 314 is upwardly projected from the inner pin ring 306b, and a cylindrical collar 313 rotatably and loosely covers the pin 314. A cap 310, in whose a large diameter head 311 is formed at an upper end, is screwed with an upper end part of the pin 314 so as to hold the collar 313.
The structures of the gear teeth of the outer pin gear are the same as those of the gear teeth 306a of the inner pin gear.
In the gear teeth of the outer pin gear and the inner pin gear, the collars 313 are engaged with outer gear teeth of the carriers and rotated around the pins 314. Therefore, frictions working to the collars 313 can be reduced, and abrasion of the collar 313 can be reduced. Namely, durability of the inner pin gear and the outer pin gear can be improved.
However, abrasion of the collars 313, which occurs from prolonged use, cannot avoid. The abraded collars 313 must be exchanged with new ones. To exchange the collar 313, firstly the cap 310 is detached from the pin 314, the abraded collar 313 is removed, the new collar 313 is attached to the pin 314, then the cap 310 is screwed again. It is troublesome for an operator to exchange the collars. Especially, in case of a large polishing apparatus, about 100 gear teeth are provided to the inner pin gear and the outer pin gear respectively, it takes a long time to exchange all of the collars 313.